1808 forum posts
Any tips on how to lower the chances of leaving marks from a chuck on semi finished items.?
Obviously one would ideally finish the job with just one chuck clamping. But of course this is not always possible is it. Sometimes the part has to be turned around.
So taking aside the obvious of not swinging on the chuck key like Thor, using soft jaws, collets etc, etc what tips do others have for lowering the chances of leaving witness marks from chucks on the work. Is it shims of brass, aluminium or are there any brands of tape that are helpful in assisting.
|198 forum posts|
I use shims cut from Diet Coke cans under the jaws
19098 forum posts
If the part is steel/brass/bronze put a bit of aluminium between each jaw and the work. For Aluminium parts use plastic, a bit of perspex or for smaller work plasticard does the job.
Some people cut a strip off a soft drinks can ( I prefer the full fat coke) which also works just watch for sharp edges
Edited By JasonB on 26/07/2014 07:30:11
|Marcus Bowman||26/07/2014 09:33:14|
|166 forum posts|
I use brass or aluminium shims, but bent so they loosely grip the jaws to prevent them falling out as I try to juggle 1 workpiece and 4 shims and a chuck key with only 2 hands. I find it also helps to seat the work against two adjacent jaws before tightening the other two, so that the jaws sit square to the work and avoid constant sideways thrust.
In a 4 jaw, lots of damage occurs because as the jaws are finally tightened the work is sometimes moved sideways to finally line up on a mark, and the gripping jaws wipe across the work surface. Shims help prevent that.
Gripping against the reversed jaws sometimes helps too, although the corners of those curved faces can be fairly sharp too.
It's also a good idea to leave a little extra material on the work, to be removed or finished later, if possible.
|Phil P||26/07/2014 13:56:43|
|668 forum posts|
A similar problem occurs when holding work in the bench vice.
I threw away the standard jaws many years ago and made a new pair out of solid aluminium alloy bar.
I also use a pair of fibre jaws when working on really delicate items.
1808 forum posts
Cheers for the replies guy's
So shims it is then.!
|John Bromley||26/07/2014 22:33:33|
|84 forum posts|
If I'm facing a piece, after parting off say, I just go round it a few times with masking tape and hold it lightly, making sure to take very light cuts.
|Ian S C||27/07/2014 10:34:06|
7468 forum posts
Of late I,v been using bits of aluminium from an old radio chassis in the lathe, and in the bench vice I often use strips of cardboard. Ian S C
|Nigel McBurney 1||27/07/2014 11:03:30|
761 forum posts
avoid the use of shim,of any material , I once saw at work an operator on the next machine to me get get his finger cut quite badly from a piece of shim used to protect the work ,it was going round in the chuck like a bacon slicer,he never did it again and neither did I ,I always use pieces of brass or aluminium which are at least 1.5 mm thick and the edges are heavily deburred with a file, another snag with shim in larger chucks,particularly four jaws is that the serrations on the jaws indent the shim and still mark the work.
regarding work in vices, where I was apprenticed all the bench vices had the hardened jaws surface ground flat, provided the jaws are kept free of filings the work does not get marked ,essential for instrument and model making ,I noticed over the years that toolmakers used solid aluminium jaws permanently fixed to the vice, mechanics tend to use bent over thick ali sheet vice clams, so that they can easily get to the serrated jaws, bodgers just muck up everything with serrated jaws, Holding delicate work in detachable fibre jaws should be avoided as they are not flat and distort the job
|Pete Gilbert 1||27/07/2014 14:36:21|
33 forum posts
Yeap, softer than the workpiece packing material is good. If you're just working with a bench vice then ally pieces or protectors are good. If you're gripping a finished ally work piece in a bench vice, either use something slightly softer (nylon sheet/block) or use spotlessly clean ally protectors.
But in a 3 jaw chuck that can make the work eccentric if you're holding on a finished dimension. Even Coke cans will vary in thickness. Basically, try to using hard lathe jaws on a finished surface if you can avoid it. I know that home engineering brings cost into play significantly more than at the workplace. But your precious work needs precision and stability at all times, if it's being turned or machined so you're better off pre machining some soft (mild steel) jaws (or collet if you can't match the work diameter) and ensuring a smooth precise gripping face that will do the gripping. A shiny surface in the jaws isn't slippery, it actually means that you've maximised the contact available for gripping the work. Perfect jaws shouldn't mark the work. Reduce pressure in the jaws and take lighter cuts.
So, if you HAVE to use what you've got, make the jaw faces as perfect as you can, or make up precision thickness packing pieces.
Edited By Pete Gilbert 1 on 27/07/2014 14:49:23
|Pete Gilbert 1||27/07/2014 14:41:58|
33 forum posts
Ouch! Was that unsupervised, or was the guy a setter/operator? Where I work, a setter would be directly responsible for something like that. We don't have operators involved in any part of the set up of any machine, unless they're being trained.
|396 forum posts|
If we're talking about holding work in a three jaw chuck, then shim is okay, but will not hold the job true and potentially the job could pull out of the chuck. A four jaw self centering chuck is the best chuck for every day turning, as the jaws have a very small surface clamping area where the clamping pressure is more evenly distributed across the four jaws, with the result of firmly clamping the work piece, while not marking the surface, even previously finish turned ones. The only time I use a three jaw chuck is to hold a hexagon.
|John Durrant||29/07/2014 21:59:05|
|44 forum posts|
For many years I used copper shims. I found the best was bits of a copper strip from a lightning conductor, but a reasonable second choice is a 12mm copper water pipe bashed flat and cut into sections. Copper between the jaw and workpiece will deform and allow you to pull in that last thou (sorry, I work in metric and still think in thou's) by tightening one jaw.
|Michael Gilligan||29/07/2014 22:28:52|
16620 forum posts
Another good source of very conveniently sized copper strip is the "slate straps" used by roofers.
I keep a few on a nail, by the bench.
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